I know the focus is on the technical aspects, but I have a small suggestion regarding art style in games:
Don't mix pixel art with fine gradients. Or more generally, don't mix pixel resolutions. If your pixel art has big chunky pixels, don't ever have a pixel smaller than that. It makes the style look inconsistent and built out of mismatching pieces.
The gradient edges could be replaced with a static edge piece, or at least a banded gradient. I know the images are probably just placeholder art, but it's something still to keep in mind.
Don't mix pixel art with fine gradients. Or more generally, don't mix pixel resolutions. If your pixel art has big chunky pixels, don't ever have a pixel smaller than that. It makes the style look inconsistent and built out of mismatching pieces.
The gradient edges could be replaced with a static edge piece, or at least a banded gradient. I know the images are probably just placeholder art, but it's something still to keep in mind.